fix(ci): use test build context for validator submitter image (#475)

## Summary
- fix the validator-set-submitter release workflow to build with
`./test` as the Docker context
- align the workflow with the Dockerfile and `test/.dockerignore`
expectations

## Testing
- docker build --no-cache -t validator-set-submitter:fix -f
./test/tools/validator-set-submitter/Dockerfile ./test
- docker run --rm validator-set-submitter:fix --help

.github/workflows/task-docker-release-validator-set-submitter.yml

@@ -89,7 +89,7 @@ jobs:
         uses: ./.github/workflow-templates/publish-docker
         with:
           dockerfile: ./test/tools/validator-set-submitter/Dockerfile
-          context: .
+          context: ./test
           registry: docker.io
           registry_username: ${{ secrets.DOCKERHUB_USERNAME }}
           registry_password: ${{ secrets.DOCKERHUB_TOKEN }}